1. Field of the Invention
The present invention relates to a vehicle control apparatus having a motor drive direction restricting means for restricting a motor drive direction, and more specifically, to an electrically-driven power steering control apparatus for assisting and urging steering operation.
2. Description of the Related Art
Conventionally, a method of preventing the rotation of a motor in an unexpected direction caused by the abnormal state and the like of a CPU is proposed by Japanese Patent Publication No. 6-51475 filed by the inventors. This method is realized by an electrically-driven power steering apparatus for assisting and urging steering operation comprising a microcomputer for outputting a motor rightward drive signal and leftward drive signal based on the output from a steering torque sensor, a motor drive direction determination circuit for outputting a rightward drive signal and leftward control signal from the output of a steering torque sensor provided with a motor control circuit unit, and an AND circuit for outputting, when the output from the microcomputer coincides with the output from the motor drive discrimination circuit, a signal for driving a motor in the direction of the coincidence.
FIG. 29 is a circuit diagram showing a motor drive direction discrimination circuit (torque direction discrimination circuit) in the conventional electrically-driven power steering control apparatus disclosed in, for example, Japanese Patent Publication No. 6-51475.
In the drawing, a torque signal is input to the inverting input terminal of a comparator CMP1 and the non-inverting input terminal of a comparator CMP2. Further, a first fixed reference voltage E1 and a second fixed reference voltage E2 which are obtained by dividing a power supply voltage Vt by resistors R1, R2 and R3 are input to the non-inverting input terminal of the comparator CMP1 and the inverting input terminal of the comparator CMP2, respectively.
Next, the operation of the circuit will be described.
The comparator CMP1 compares the torque signal t with the reference voltage E1 and when t&gt;E1, the output Ex1 of the comparator CMP1 is at an L level. Whereas, when t&lt;E1, the output Ex1 is at an H level.
Likewise, the comparator CMP2 compares the torque signal t with the reference voltage E2, and when t&gt;E2, the output Ey1 of the comparator CMP2 is at the H level. Whereas, when t&lt;E2, the output Ey1 is at the L level.
When the output Ex1 of the comparator CMP1 is at the H level, a rightward output is prohibited. Likewise, when the output Ey1 of the comparator CMP2 is at the H level, a leftward output is prohibited.
FIG. 30 is a view explaining a motor output and the operation of the torque direction discrimination circuit.
In the figure, a relationship T4&lt;T1&lt;T0&lt;T2&lt;T3 is established in torques from T0 to T4. The torque signal t&lt;T0 results in a leftward torque, the torque signal t&gt;T0 results in a rightward torque and the torque signal t=T0 results in neutral. When the torque signal t is between T2 and T3 or between T4 and T1, a value proportional to the torque signal t is determined as the motor output, when the torque signal t is equal to or less than T4 or larger than T3, the motor output is fixed to the maximum value Imax of a motor output current and when the torque signal t is between T1 and T2, the motor output becomes zero. Further, the relationship between torque determination reference values E1.sub.T and E2.sub.T corresponding to the reference voltages E1 and E2 of the torque direction discrimination circuit, respectively and the torque signals T1 and T2 are set to T1&lt;E2.sub.T &lt;E1.sub.T &lt;T2. With this arrangement, when a torque is equal to or less than the reference value E1.sub.T, motor rightward drive is prohibited and when a torque is larger than the reference value E2.sub.T, motor leftward drive is prohibited. Further, when a torque is between the reference value E1.sub.T and E2.sub.T, both of rightward and leftward motor drive are prohibited.
The substitution of the non-inverting input terminals for the inverting input terminals of the comparators CMP1 and CMP2 of the torque direction discrimination circuit results in a torque direction discrimination circuit or a motor drive direction discrimination circuit as shown in FIG. 31.
In the drawing, the torque signal t is input to the non-inverting input terminal of a comparator CMP3 and the inverting input terminal of a comparator CMP4. Further, a third fixed reference voltage E3 and a fourth fixed reference voltage E4 which are obtained by diving the power supply voltage Vt by the resistors R1, R2 and R3 are input to the inverting input terminal of the comparator CMP3 and the non-inverting input terminal of the comparator CMP4, respectively.
Next, the operation of the circuit will be described.
The comparator CMP3 compares the torque signal t with the reference voltage E3 and when t&gt;E3, the output Ex2 of the comparator CMP3 is at an H level. Whereas, when t&lt;E3, the output Ex2 is at an L level. Likewise, the comparator CMP4 compares the torque signal t with the reference voltage E4 and when t&gt;E4, the output Ey2 of the comparator CMP4 is at the L level. Whereas, when t&lt;E4, the output Ey2 is at the H level.
When the output Ex2 of the comparator CMP3 is at the L level, a leftward output is permitted. Likewise, when the output Ey2 of the comparator CMP4 is at the L level, a rightward output is permitted.
FIG. 32 is a view explaining a motor output and the operation of the torque direction discrimination circuit.
In the drawing, a relationship T4&lt;T&lt;T0&lt;T2&lt;T3 is established in torques from T0 to T4. The torque signal t&lt;T0 results in a leftward torque, the torque signal t&gt;T0 results in a rightward torque and the torque signal t=T0 results in neutral. When the torque signal t is between T2 and T3 or between T4 and T1, a value proportional to the torque signal t is determined as the motor output, when the torque signal t is equal to or less than T4 or larger than T3, the motor output is fixed to the maximum value Imax of a motor output current and when the torque signal t is between T1 and T2, the motor output becomes zero. Further, the relationship between torque determination reference values E3.sub.T and E4.sub.T corresponding to the reference voltages E3 and E4 of the torque direction discrimination circuit, respectively and the torque signals T1 and T2 is set to E4.sub.T &lt;T1&lt;T2&lt;E3.sub.T. With this arrangement, when a torque is equal to or less than E3.sub.T, motor leftward drive is permitted and when a torque is larger than E4.sub.T, motor rightward drive is permitted. Further, when a torque is between the reference value E3.sub.T and E4.sub.T, both of rightward and leftward motor drive are permitted.
Since the conventional apparatus is arranged as described above, it has the following problem.
That is, the torque determination reference values E1.sub.T to E4.sub.T are fixed in the conventional apparatus. As a result, when the motor drive direction determination level (torque determination reference value) of a steering torque as the torque signal t is represented by E1.sub.T, E2.sub.T (E2.sub.T &lt;E1.sub.T), motor drive direction restricting means including the torque direction discrimination circuit prohibits motor rightward drive when the steering torque t satisfies t&lt;E2.sub.T and prohibits motor leftward drive when the steering torque satisfies E1.sub.T &lt;t. Further, when the steering torque t satisfies E2.sub.T .ltoreq.t.ltoreq.E1.sub.T, there are two methods of permitting motor drive (hereinafter, referred to as neutral permission) and prohibiting motor drive (hereinafter, referred to as neutral prohibition). The neutral permission has characteristics shown in FIG. 32 and the neutral prohibition has characteristics shown in FIG. 30.
In the neutral prohibition, even if a steering wheel is released from a hand in an abnormal motor output (steering torque is neutral), since motor drive is prohibited, inconvenience such as the self-turn (unintentional rotation) of the steering wheel and the like is not caused and safety is secured. However, when a steering torque is within the neutral determination region (for example, when the steering wheel is released), since the motor drive direction restricting means prohibits motor drive, the motor cannot be controlled. That is, since there is a problem that a motor control cannot be executed in the neutral prohibition, the motor cannot be controlled with redundancy.
Further, the motor drive direction determination levels E1.sub.T, E2.sub.T must be set to T1&lt;E2.sub.T &lt;E1.sub.T &lt;T2 From FIG. 30. This is because that when the motor drive direction determination levels E1.sub.T, E2.sub.T are set to E2.sub.T &lt;T1&lt;T&lt;E1.sub.T, since a motor output is prohibited by the motor drive direction restricting means between E2.sub.T and T1 and between T2 and E1.sub.T, there is a problem that a motor current causes hunting. To cope with this problem, when the motor drive direction determination level is composed of an H/W, resistors and the like require pinpoint accuracy, and thus the cost of the H/W composed of the resistors and the like of pinpoint accuracy is increased.
Furthermore, since motor drive is prohibited when a steering torque is within the neutral determination region, there is a lack of an assisting force when the motor is driven so that when the steering wheel states to be cut, it is felt heavy. That is, the motor drive prohibition adversely affects the feeling in steering operation when a torque is neutral.
In addition, in the neutral permission, even if a steering torque is within the neutral determination region (between T1 and T2), a motor can be driven and thus the motor control can be executed with redundancy. However, since the motor can be driven even if a steering torque is within the neutral determination region, when the steering wheel is released from a hand in an abnormal motor output, there is possibility that the steering wheel turns by itself. To avoid the occurrence of a steering wheel self-turn mode and the like, the neutral permission region is conventionally set to a narrow region, wherein a problem that the neutral permission region cannot be set in a wide range.
An object of the present invention made to overcome the above problems is to provide a vehicle control apparatus having both of the redundancy of a motor control as an advantage of neutral permission and the safety as an advantage of neutral prohibition by changing a steering force determination level and further capable of increasing the range of a neutral permission region and driving a motor even in a neutral prohibition region.